Immediate hypersensitivity to allergens is very common among children and young adults with asthma and rhinitis. Sensitization to one or more of the major indoor allergens (such as dust mite, cat, dog, or cockroach), combined with significant accumulation of relevant allergens in the house, has been consistently found to be the strongest risk factor for asthma in population, case control, and prospective studies [1-5]. It is important to remember that there are major differences in the dominant allergens based on climate, housekeeping practices, and pet ownership. In particular, there are now well-defined areas where dust mite, cockroach, or pet dander is the strongest contributor to asthma risk. It is possible that certain indoor allergens, such as dust mite, are more important in the pathogenesis of allergic airway disease than others, and this is an area of active investigation [6-9]. (See "Risk factors for asthma".)

Further evidence for a causal relationship between allergen exposure and asthma comes from bronchoprovocation experiments demonstrating that these allergens can induce bronchospasm, eosinophilic airway inflammation, and prolonged increases in bronchial hyperreactivity [10,11]. Perhaps more significantly, moving some asthmatic children or adults from their homes to a different, low allergen residential setting results in major improvements in clinical symptoms and bronchial hyperreactivity [1,12-14]. This background provides a powerful rationale for recommending that allergic patients should reduce allergen exposure in their houses as part of the management of asthma and allergic rhinitis [15].

Specific monoclonal antibody-based assays have been developed to monitor allergen levels during controlled trials and to test the specific measures recommended to control exposure to mite, cat, dog, and cockroach antigens [16-18]. These techniques have facilitated detailed studies of specific allergens and have helped to define effective control measures, although the exquisite specificity of these measurements may mean that some forms of the specific allergen (eg, some isoforms of Der p 1) may escape detection [19].

GENERAL PRINCIPLES

Allergen avoidance is appropriate for symptomatic patients with allergic responses documented either with positive skin tests or serum assays for specific IgE antibodies. Once specific sensitivities have been defined, it is important to implement a comprehensive environmental control plan for all, or as many as possible, of the allergens that are relevant to that patient. Studies in which environmental control has been most effective are those in which the specific measures taken were tailored to the patient and addressed the major allergens to which each patient was sensitized [20,21].

Urban children with moderate-to-severe asthma represent a population that has been studied with regard to the impact of environmental allergen control on asthma. Comprehensive environmental modification in these children has been shown to be effective in reducing asthma symptoms and appears to be cost effective if carefully performed [20,22].

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